Comparing IncobotulinumtoxinA (Xeomin®) and OnabotulinumtoxinA (Botox®): Identical Potency Labelling in the Hemidiaphragm Assay

Botulinum toxin (BT) is provided by several manufacturers producing a number of different drugs. Their potency is given in internationally standardised mouse units (MU). Clinical practise, however, reveals that the potency labelling of different BT drugs may not be identical. We wanted to use the mouse diaphragm assay (MDA) to compare the two BT drugs onabotulinumtoxinA (ONA) and incobotulinumtoxinA (INCO). For this, we measured the paresis time (PT) of different ONA or INCO doses. All BT came from several different and unexpired drug batches. PT for 20MU were 169.7 ± 28.9 min (ONA) and 132.3 ± 1.5 min (INCO) (p = 0.089), for 60MU 105.3 ± 10.1 min and 84.7 ± 4.2 min (p = 0.031), for 100MU 69.7 ± 1.5 min and 66.0 ± 7.0 min (p = 0.462) and for 140MU 74.7 ± 0.6 min and 62.3 ± 2.1 min (p = 0.100), respectively. The overall PT were 104.8 ± 12.5 and 86.3 ± 8.5 min (p = 0.178). Results presented here do not reveal differences in potency labelling between ONA and INCO, even when the full range of therapeutic doses are examined, although there was a trend towards stronger INCO effects. Data confirm previous reports on identical potency labelling of ONA and INCO. The MDA seems to be an appropriate instrument to test the potency labelling of other BT drugs as well, including new BT drugs currently under development.